This invention relates to an ultrasonic diagnosing apparatus including an improved high-speed sector scanner adapted to effect a high-speed sector scan by an ultrasonic probe.
When a tomographic image corresponding to the human heart is obtained, during the transmission of ultrasonic waves the presence of the ribs of a human being tend to block the transmission of some of the ultrasonic waves. In order to prevent such an influence from the ribs, a method for scanning often includes bringing an ultrasonic probe (a device for transmitting and receiving ultrasonic waves to obtain ultrasonic echoes) into the closest possible proximity to the body surface of a human being and effecting scanning so as to send ultrasonic pulses from a position between the ribs.
In order to transmit ultrasonic pulses from a position between the ribs toward the heart of the human being, it is very effective to effect a sector scanning by an ultrasonic probe, by rotating the probe in a sector fashion. Sector scanning is effective because that the inter-rib spacing is very narrow. Since the human heart is constantly pulsated, no good-quality tomographic image corresponding to the heart can be obtained unless ultrasonic echoes are captured through high-speed sector scanning.
Conventionally, an ultrasonic high-speed sector scanner for effecting a high-speed sector scanning has been used.
FIG. 1 is a schematic diagram showing a conventional scanner. Reference numeral 1 shows a shaft. At both end portions the shaft 1 is supported by corresponding bearings 2, 2'. The number 3 shows a probe holder mounted on the shaft 1, and an ultrasonic probe 4 is held by the probe holder 3. The number 5 shows a pulley fixedly mounted on the shaft 1. The number 6 shows a motor; 7 shows a drive side pulley connected to the motor 6 so that it is rotatably driven; 8 shows a belt run between the drive side pulley 7 and the pulley 5; and 9 shows a bearing. The motor 6 is forwardly and reversely rotated in a repetitive fashion. Since the pulley 7 is mounted on the shaft of the motor and the belt 8 is run between the pulley 7 and the pulley 5, the shaft 1 can be forwardly and reversely rotated through such a mechanism. The ultrasonic probe 4, mounted on the probe holder 3 which is on the shaft 1, effects an oscillating movement to effect a sector-scanning.
The above-mentioned apparatus effects a sector scanning through the forward and reverse rotation of the motor 6, thus providing a bar to the obtainment of a high-speed apparatus. Furthermore, the motor requires a great torque, making the apparatus bulky as a whole.
When ultrasonic pulses are emitted from a position between the ribs toward the heart of the human being, the ultrasonic wave transmit/receive surface of a container including a sector scanner (FIG. 1) and ultrasonic wave transmitting medium has to be contacted with an inter-rib surface portion of the human body. Furthermore, the apparatus including such a container needs to be made compact and light in weight.
Another apparatus is also known which is adapted to convert the rotational motion of a motor to a repetitive, rotational motion so as to obtain a sector movement. Such an apparatus lacks the smoothness of conversion to the repetitive, rotational movement, making it difficult to obtain a greater sector angle (an oscillation angle of the ultrasonic probe). Moreover, it is also difficult to detect the position corresponding to a scanning angle required for the presentation of an image. Thus, it would be difficult to correctly display an ultrasonic tomographic image, as well as to adjust the sector angle.
The adjustment of the sector angle of the ultrasonic probe is very important in obtaining a tomographing heart image. For example, if the number of tomographic images as displayed during one second is fixed, the number of scanning lines corresponding to one tomographic image does not vary for a greater sector angle, because the speed of the ultrasonic wave is fixed. Thus, a very coarse image is displayed on the screen of a monitor device. If, on the other hand, the sector angle is smaller, a fine, good-quality tomographic image can be obtained. When, however, scanning is started at a smaller sector angle, only one portion of the heart of the human being is displayed as an image, and it would be difficult to locate that heart region required for diagnosis. It would be also difficult to associate this region with other regions. In order to quickly locate a region of interest (ROI) of the heart for effective diagnosis, it is necessary to observe a wider range of image at a wider sector angle, to quickly and accurately locate the ROI of the heart from the overall point of view. It is then necessary to obtain a good-quality image, at a narrow sector angle, which corresponds to only the ROI of the heart. In the conventional apparatus it would be difficult to adjust the sector angle at will.